#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
#include <math.h>
#include <string.h>
using namespace std;

#define ROW 26*26
#define COL 7

char s[] = "aaa";
char str[ROW][COL] = { '\0' };

int main()
{
	int L = 2;
	int num = 555;
	//scanf("%d %d", &L, &num);

	int count = 0;
	int NUM = (int)pow(26, L);
	int tem = NUM;
	
	while (tem--)
	{

		strcpy(str[count], s);
		*(s + 2) = *(s + 2) + 1;
		count++;

		int l = 0;
		while (l++ < L)
		{
			if (count %(int)(pow(26, l)) == 0 && count != 0)
			{
				
				*(s + 3 - l) = 'a';
				*(s + 2 - l) = *(s + 2 - l) + 1;							
			}
		}
	}
	
	printf("%s", str[NUM - num ]);

	return 0;
}
